Collimator for high energy radiation

ABSTRACT

A plurality of cells are disposed in an aperture insert which is receivable in an aperture of a collimator for high energy radiation. The cells can be selectively filled with radiation shielding material.

United States Patent [191' Barthel et al.

[451 Apr. 16, 1974 COLLIMATOR FOR HIGH ENERGY RADIATION [75] Inventors: Rolf Barthel, Frankfurt am Main;

Bernd-Peter Offermann, Hamburg, both of Germany [73] Assignee: Licentia Patent-Verwaltungs-G.m.b.H., Frankfurt, Germany [22] Filed: Apr. 17, 1972 [21] Appl. No.: 244,554

[30] Foreign Application Priority Data Apr. 16, 1971 Germany 2118426 [52] US. Cl. 250/512 [51] Int. Cl. G031) 41/16 [58] Field of Search 250/ 105 [56] References Cited UNITED STATES PATENTS 3,407,300 10/1968 Hansen 250/105 2,871,367 1/1959 Gournay 3,114,043 12/1963 Thomas 250/105 Primary Examiner--James W. Lawrence Assistant Examiner-C. E. Church Attorney, Agent, or Firm-Spencer & Kaye 57 7 ABSTRACT A plurality of cells are disposed in an aperture insert which is receivable in an aperture of a collimator for high energy radiation. The cells can be selectively filled with radiation shielding material.

5 Claims, 5 Drawing Figures RESERVOIR COLLIMATOR FOR HIGH ENERGY RADIATION BACKGROUND OF THE INVENTION The present invention relates to a collimator for high energy radiation particularly a collimator made of a radiation shielding material to shield the radiation source, disposed in its interior, against environmental influences and which is provided with an aperture for the passage of the useful radiation.

Neutron collimators are known for neutron therapy and in these devices the beams of useful radiation are directed through aperture inserts having different size openings. Different aperture inserts are kept in readiness in the treatment room. Since the aperture inserts sometimes are very heavy (50 to 100 kg) often they can be placed into the collimator only with the aid of lifting devices. Furthermore a replacement of the aperture insert can take place only after the collimator has been placed in a certain position. This operation is time consuming and necessarily requires some skill on the part of the operating personnel.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a collimator for high energy radiation which enables automatic radiation treatment with variable radiation beam cross sections to be accomplished without an exchange of aperture inserts.

This is accomplished by the present invention through the use of an aperture system which is formed of a plurality of cells that can be selectively filled with a shielding material. In such an aperture system the walls of the individual cells must be kept as thin as possible and the cell walls must be provided with a layer of material having minimum adhesion properties. I

To vary the shape and size of the exiting beam of useful radiation, a hose or tube line, provided with valves, may be connected to each cell so that a suitable radiation shielding material can be inserted into, or drawn out of the cells. Such a material may be a highly viscous liquid, emulsion or paste or a powdery and/or granual substance.

A particular advantage of the collimator according to the present invention is that a special aperture insert permits a plurality of different useful radiation beam configurations to be emitted without it being necessary to exchange aperture inserts and increase the required layer thickness for the shielding.

Furthermore this special aperture insert provides substantiallymore possible variations in the shapeand size of irradiation fields. A controlled introduction of the shielding material into the individual cells permits variation of the energy dosage in the individual sections of the irradiation field and makes it possible to have the doses homogeneous over the entire irradiation field and to compensate for marginal effects.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 5 shows a cross-sectional detail view of a physical connection for a hose to one cell of the aperture system.

DESCRIPTION OF THE PREFERRED EMBODIMENT As seen in FIG. 1, the neutron collimator generally indicated at 1, is provided, in a usual manner, with the radiation tube 1' of an ion accelerator not shown, and a target 2 forming the neutron source. The target 2 is disposed in the center of a cylindrical collimator block indicated generally at 3. The collimator block 3 preferably consists of a plurality of, for example three, concentric annular layers. The first layer decelerates the high energy neutrons, the second layer further decelerates and absorbs the dispersed neutrons, and the third layer absorbs the resulting gamma rays. As this particular construction forms no part of the invention, and in order to simplify the drawing, these layers are not shown in detail.

The shielding of neutrons in the collimator is particularly effective if the collimator is constructed of a plurality of layers and, for example, the first and third layers consists of steel and the second layer is of a material having a high hydrogen content per unit of volume. In order to reduce the captured high energy hydrogen and iron radiation, the second and third layers also contain boron additives.

As indicated generally in FIG. 1, the collimator block 3 has an opening 4 for receiving the aperture system 5, used to isolate the useful neutron beam. The aperture system 5 is formed by a plurality of inwardly tapering cells 5' that are rectangular in shape at their base surfaces and which extend in a region that is situated between a point adjacent the target 2 and a point at the exterior of the collimator block 3. When the aperture system 5 is disposed in aperture 4 the cells converge toward the interior of the collimator 1. The thickness of the wall 5" of each cell 5' is made as thin as possible and these walls are provided with a layer of material, not shown, having minimum adhesion properties.

FIG. 2 shows one manner in which the aperture system 5 is carried in an apertuer insert aperture that is adapted to be inserted into the opening 4 of the collimator 1. This aperture insert 6 includes a peripheral shielding 7 of suitable material which surrounds the aperture system 5. This shielding 7 is provided along its outer periphery with steps and protrusions which prevent passage of stray radiation through the opening 4 of the collimator.

Each one of the plurality of closed cells 5' is connected with hoses or tubular lines 8 through which, via valves 9, a suitable material, which provides good shielding against the radiation, is selectively forced into the cells from a reservoir 10, or subsequently removed from the cells to reservoir 10, with the aid of pumps 11..

FIG. 5 shows one specific manner in which a physical connection for a hose 8 is made to a cell 5' of the aperture system 5. The cell 5' is sealed by a bottom plate 5" which has a bore for the inlet and a second bore, not shown here, for the outlet of the shielding material. A pipe connection 13 has been welded to the bottom plate 5" above its bore. Over the pipe connection 13 the end of the hose 8 has been pushed. The hose end pushed over the pipe connection 13 could additionally be secured by a hose clip.

It would also be possible to use in place of the permanent connection shown in the drawing, such a connection which could quickly and easily be detached after filling up the shielding material, so that the handling of the collimator during the operation will not be disturbed. For this purpose a quick release fastener for a hose with check valve installed could be provided as very often used to connect garden hoses to water pipes.

The shielding material may be a liquid which is more or less viscous at normal or increased temperatures, an emulsion, a paste, and/or a powdery and/or granual substance. Examples of suitable shielding materials are oils, water, paraffins and other plastics, pastes consisting of a plastic and iron and/or lead powder and other additives, powdered lead, powdered iron, etc. This substance may harden, for example, when it reaches the cells and may be heated again and pumped out when the irradiation field pattern is to be changed.

An example for a substance of this type is paraffin which hardens at normal temperatures and may easily be softened by heating so that it can be pumped out of the cells In order to heat the hardened paraffin, the walls 5" of the cells 5' may be provided with heating conductors or heating mats.

The layer of material with minimum adhesion properties, e.g., a Teflon layer, on the cell walls 5" must assure complete removal of the shielding material from the individual cells 5.

FIGS. 3 and 4 show the raster field pattern resulting from irradiation through the aperture system according to the present invention. Each rectangle in the raster field is a reproduction of the lower base surface of one of the plurality of cells 5' as seen when looking into the collimator 1. If none of the individual cells is filled with shielding material from the reservoir 10, the entire useful radiation beam from radiation source 2 emerges out of the aperture opening 4 through the aperture system 5. This case is shown in FIG. 3.

If, however, the irradiation field is to have a certain shape and size, the corresponding number of cells of the aperture system 5 is filled with shielding material. In this situation, the cells which have been filled are shown, for example, by hatching in FIG. 4. It will be appreciated that the rays.,now pass only through the other cells, which are free'of the shielding material, to the irradiation field.

The degree to which the individual cells are filled also servesto vary the energy dosage in the individual areas of the irradiation field It is thus advantageously possible to make the doses homogeneous over the entire irradiation field and to compensate for marginal effects.

With the aid of a collimator according to the present invention it is possible to perform fully automatic radiation therapy operations. In particular, the radiation field can be adapted to the object to be irradiated with relative accuracy and ease even when it has an irregularly shaped outline.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

We claim:

1. In a collimator for high energy radiation including a radiation shield permanently surrounding and shielding a high-energy radiation source disposed in the interior of the collimator, an aperture in the radiation shield for the passage of a beam of useful radiation from the source, the improvement comprising in combination:

a. means disposed in said aperture for defining therein a plurality of cells that divide the cross section of said aperture into a raster pattern, each of said cells extending in a region situated between a point adjacent said source and a point at the exterior of said shield; and

b. conduit and valve means connected to each of said cells for introducing a radiation shielding material into and withdrawing the same from selected ones of said cells, and. for varying the cross section of said beam.

2. An arrangement as defined in claim 1 wherein the cross-sectional area of said cells progressively decreases toward the interior of the collimator.

3. An arrangement, as defined in claim 1 wherein each of said cells has relatively thin walls and said walls have a layer of a material having minimum adhesion properties.

4. An arrangement as defined in claim 1, wherein said radiation shielding material which is introduced into and removed from said cells is a non-gaseous fluid.

lar form.

* l I I 

1. In a collimator for high energy radiation including a radiation shield permanently surrounding and shielding a highenergy radiation source disposed in the interior of the collimator, an aperture in the radiation shield for the passage of a beam of useful radiation from the source, the improvement comprising in combination: a. means disposed in said aperture for defining therein a plurality of cells that divide the cross section of said aperture into a raster pattern, each of said cells extending in a region situated between a point adjacent said source and a point at the exterior of said shield; and b. conduit and valve means connected to each of said cells for introducing a radiation shielding material into and withdrawing the same from selected ones of said cells, and for varying the cross section of said beam.
 2. An arrangement as defined in claim 1 wherein the cross-sectional area of said cells progressively decreases toward the interior of the collimator.
 3. An arrangement as defined in claim 1 wherein each of said cells has relatively thin walls and said walls have a layer of a material having minimum adhesion properties.
 4. An arrangement as defined in claim 1, wherein said radiation shielding material which is introduced into and removed from said cells is a non-gaseous fluid.
 5. An arrangement as defined in claim 4, wherein said radiation shielding material is in powdeRy or granular form. 